[英]F# match with ->
I want to make something like it (Nemerle syntax) 我想做类似的东西(Nemerle语法)
def something =
match(STT)
| 1 with st= "Summ"
| 2 with st= "AVG" =>
$"$st : $(summbycol(counter,STT))"
on F# so is it real with F#? 在F#上,F#真的如此吗?
There is no direct support for that but you can mimic the effect like this as well: 没有直接的支持,但你也可以模仿这样的效果:
let 1, st, _ | 2, _, st = stt, "Summ", "AVG"
sprintf "%s %a" st summbycol (counter, stt)
If I understand you correctly, you'd like to assign some value to a variable as part of the pattern. 如果我理解正确,你想为变量分配一些值作为模式的一部分。 There is no direct support for this in F#, but you can define a parameterized active pattern that does that: 在F#中没有对此的直接支持,但您可以定义参数化的活动模式来执行此操作:
let (|Let|) v e = (v, e)
match stt with
| Let "Summ" (st, 1)
| Let "AVG" (st, 2) -> srintf "%s ..." st
The string after Let
is a parameter of the pattern (and is passed in as value of v
). Let
之后的字符串是模式的参数(并作为v
值传入)。 The pattern then returns a tuple containing the bound value and the original value (so you can match the original value in the second parameter of the tuple. 然后该模式返回一个包含绑定值和原始值的元组(因此您可以匹配元组的第二个参数中的原始值。
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